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Please check my *better* design, 48V 225A

balachai

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Mar 13, 2021
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How does this look?
48V system 1d.jpg

I realised that a 100/20 charge controller can feed 48V to the battery while keeping solar voltages below 120V. That's enabled me to switch from 24V to 48V battery voltage, which simplifies everything and reduces currents, compared to my previous design. Cells are new from a local store offering an 8-year warranty to 80% SOH.
 
BUMP :D

Nice mockup - I'd like to know what people think about this 48v setup also, esp if you're springin for Victron parts.
 
Thanks for the bump boondock :) My build is coming together, the main change is the battery cable is 70mm2 instead of 95mm2. Hopefully that'll be OK 'cause if the current approaches 225 Amps, it wont' be that high for long. Also I couldn't find Mega fuses below 100A that were rated for 48V nominal operation, so I've had to go for a higher current fuse to the DC loads.

Oh and the panels might be 370W rather than 330W. The array short-circuit current of ~22A will slightly exceed specs for the 100/20 charge controller (max input current 20A), but hopefully that'll be OK.
 
I hadn't anticipated the 48v fuses being a problem, thanks for learnin me up. I'd ike to know what you purchased and also the exact 370w panels if you have them already. Do you have a parts list in a doc or excel etc?
 
I hadn't anticipated the 48v fuses being a problem, thanks for learnin me up. I'd ike to know what you purchased and also the exact 370w panels if you have them already. Do you have a parts list in a doc or excel etc?
I haven't got the panels yet, but I'm looking at Jinko Tiger JKM370M-60HLM. Sorry, I'm not organised enough for a parts list. :)
 
what will this be used in? you are stepping down to 24vdc
 
I'd move the manual battery disconnect to be right after the battery fuse, and then the main contactor. I don't like anything except the fuse seeing power when I have it manually turned off.
 
I realised that a 100/20 charge controller can feed 48V to the battery while keeping solar voltages below 120V
You mean "by keeping solar voltages below 100V", right? 120V will damage this MPPT, and at cold temperatures two 45V Voc panels might fry it too! Temperature coefficients for Voc are usually a bit less than 100mV/degC, so if nominal spec is 25C you should check on that with your actual panel specifications.

That MPPT can handle roughly 1kW of solar (20A * 48V output to battery). That's not a whole lot of solar power for what looks like a 16.7kWh battery. At 5 hours insolation per day, you would need 3.34 days with zero load usage to charge the battery from empty. That might be fine depending on your planned usage. But, if you're looking for a change to make I would get a bigger MPPT to start with rather than upgrade it down the line if/when you add more panels.
 
You mean "by keeping solar voltages below 100V", right?
Yeah it's only 2 panels in series so it'll be below 100V.

That MPPT can handle roughly 1kW of solar
It can handle more than that - you can oversize the panel power and it'll clip its production. I'm starting with 2 of these MPPTs with future expansion to 4 as noted in the schematic.
 
I'd move the manual battery disconnect to be right after the battery fuse, and then the main contactor. I don't like anything except the fuse seeing power when I have it manually turned off.
Yeah that's valid. My thinking was that the contactor is kinda "part of the battery" as it's controlled by the BMS.
 
It can handle more than that - you can oversize the panel power and it'll clip its production.
Yep, as long as you’re aware it can only pass about 1kW (manual says 1160W). It will “tolerate” more solar but not use more than that or pass more than that to the battery, which is why I said it’s undersized for the battery capacity, in my opinion. Anyway, seems like we are saying the same thing.
 
Yeah that's valid. My thinking was that the contactor is kinda "part of the battery" as it's controlled by the BMS.

Yes true, but try to think of it as a "valve" that the BMS can open to protect the battery. That valve just needs to be before any charge/discharge sources.

It can also be two valves as the safety for discharge is a bit different that for charge (cold temp cutouts, and LVD on discharge but HVD on charge)
 
think of it as a "valve" that the BMS can open to protect the battery. That valve just needs to be before any charge/discharge source
Yep!

It can also be two valves as the safety for discharge is a bit different that for charge (cold temp cutouts, and LVD on discharge but HVD on charge)
I'm going to cover that with communication from the REC BMS to the Victron gear via CAN-bus. The BMS can tell the Victron gear to stop charging the battery in cold temps, while still leaving the contactor open to allow discharge. Apparently it's even smart enough to allow the solar charge controllers to generate enough power to supply loads in cold weather, while not pushing current into the battery. So the contactor only operates during a true problem condition.

Oh another thing - I can manually turn off the contactor by switching off the BMS with its little manual switch.
 
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I don't think you need the second set of breakers between the MPPT and the Lynx unless accessibility to the breakers between the solar panels and the MPPT is an issue.
 
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